BSCPH304 Board of Studies and Programme Coordinator Board of Studies Prof. P. D. Pant Prof. S.R. Jha, Director School of Sciences School of Sciences, I.G.N.O.U., Maidan Uttarakhand Open University, Haldwani Garhi, New Delhi Prof. Dr. P. S. Bisht, Prof. R. C. Shrivastva , SSJ Campus, Kumaun University, Almora. Professor and Head, Department of Physics, Dr. Kamal Deolal CBSH, G.B.P.U.A.&T. Pantnagar, India Department of Physics School of Sciences, Uttarakhand Open University Programme Coordinator Dr. Kamal Deolal Department of Physics School of Sciences, Uttarakhand Open University Unit writing and Editing Editing Writing Dr. Kamal Deolal Dr. Vijendra Lingwal Department of Physics Department of Physics School of Sciences, Uttarakhand Open University Pt. L.M.S. Government PG College Rishikesh Dehradun, Uttarakhand, India. Dr. D K Upreti Department of Physics, Govt PG College, Ranikhet Almora Course Title and code : Experimental Physics III (BSCPH304) ISBN No. : Copyright : Uttarakhand Open University Edition : 2019 Published by : Uttarakhand Open University, Haldwani, Nainital- 263139 Printed by : 2 BSCPH304 BSCPH-304 Experimental Physics III DEPARTMENT OF PHYSICS SCHOOL OF SCIENCES UTTARAKHAND OPEN UNIVERSITY Phone No. 05946-261122, 261123 Toll free No. 18001804025 Fax No. 05946-264232, E. mail [email protected] htpp://uou.ac.in 3 BSCPH304 Contents Course 10: Experimental Physics III Course code: BSCPH304 Credit: 3 Unit Experiment Page number number 1 To draw the characteristics of vacuum diode valve 1 2 To draw characteristics of triode valve 7 3 To draw the characteristics of tetrode valve 16 4 To verify-Child Langmuir law of space charge limited current using 22 diode valve 5 To draw characteristics of PN junction diode 29 6 To plot the characteristics of Zener diode and study of Zener diode as a 38 voltage regulator 7 To draw output characteristics of NPN transistor in common emitter 45 configuration 8 To draw output characteristics of PNP transistor in common base 51 configuration 9 To measure the hybrid parameters of PNP transistor in common 57 emitter configuration 10 To plot output characteristics of FET and measure pinch off voltage 64 11 To verify Thevenin’s theorem 70 12 To verify maximum power transfer theorem 76 13 To study of RC coupled amplifier 82 14 To study of TC coupled amplifier 88 15 To draw characteristics of photoelectric cell 94 16 To study of power supply 101 17 To study the logic gates 109 18 To verify truth table of adder and subtractor 121 19 Study of Cathode Ray Oscilloscope (CRO) 130 4 BSCPH304 20 Study of He-Ne Laser (To Determine the Wavelength of He-Ne Laser 138 Using Diffraction Grating) 21 To Measure Specific Charge (e/m) of an Electron by Helical Method 146 22 To determine the value of Planck’s constant h by a photo cell 154 23 To find out the value of energy band gap in semiconductor using a PN 163 junction diode 24 Study of hydrogen spectra and Rydberg Constant 169 5 BSCPH304 Experiment 1: To draw the characteristics of vacuum diode valve Structure 1.1 Objectives 1.2 Introduction 1.3 Apparatus Used 1.4 Theory and Formula Used 1.5 About apparatus 1.6 Procedure 1.7 Observation 1.8 Calculation and Discussion 1.9 Result 1.10 Precaution and source of error 1.11 Summary 1.12 Glossary 1.13 References 1.14 Viva-voce questions and Answers 1 BSCPH304 1.1 Object : After performing this experiment, you should be able to • What are vacuum tubes specially diode • Working of diode • How characteristics of diode valve is drawn 1.2 Introduction: Diode valve is a vacuum tube having two electrodes namely plate and cathode inside evacuated glass tube. It works on the principle of thermionic emission. For the proper use of the diode valve plate is kept at high potential with respect to cathode. When cathode of diode is heated by passing current in it, the cathode emits electrons. These electrons are collected by plate, which is at positive potential with respect to cathode. Electrons flow from cathode to plate, thus plate current flows in plate circuit. As plate voltage increases the plate current also increase. The current in circuit is controlled by plate and grid potentials. The plate current flows in the circuit only when plate is positive potential with respect to cathode and direction of flow of electron is always from cathode to plate never plate to cathode. Because of this unidirectional flow of current, diode is called ‘diode valve’. At constant temperature of cathode the variation of plate current with the plate voltage is non linear and plate current is controlled by space charge. The current is called space charge limited current. When the temperature of cathode is increased, more electrons are emitted from cathode hence increase in saturated plate current . 1.3 Apparatus Used: The diode valve, 6.3 volt heating filament (cathode), high tension source for plate (around 250V), voltmeter (0-250V) , milliammeter (0-10 mA) and Rheostat (100Ω), connection wires. 1.4 Theory and Formula Used : Diode valve is two electrode namely plate and cathode. When cathode of the diode valve is heated, the electrons are emitted from the surface of cathode. The number of electrons emitted depends on temperature of the cathode. The first group of emitted electrons gathers in the space surrounding the cathode. It exerts repealing electrostatic force to next emitted electrons, which therefore start to return to cathode. Their return is however prevented by next group of emitted electrons. Thus the dense cloud of electron is formed in space around cathode. This electron cloud is called space charge. This space charge repeals the further emitted electron. When plate is given small positive potential, some of the electrons near the plate is attracted by plate and constitute current. If we further increase plate potential, the plate current also increases. This current only depends on space charge, plate potential and independent of temperature of cathode. 2 BSCPH304 When plate voltage is increased, the plate current also increases. This variation is not linear, and current is called space li mited plate current. If the plate voltage is further increases, the current become maximums called saturated current. This happens when plate voltage is enough high to attract all electrons emitted by cathode. At this stage, the saturated current can only increased by increasing temperature of cathode. This saturated current is called temperature limited current. 1.5 About apparatus : Diode valve is a vacuum tube having two electrodes namely plate and cathode inside evacuated glass tube as shown in figure 1 . Cathode, which serve as source of electrons is an indirectly heated oxide-coated nickel cylinder. Cathode is heated indirectly by insulated heater filament enclosed within it. The plate is also hollow cylinder made of nickel, molybdenum or iron and surrounds the cathode. The apparatus in the experiment is a simple electric circuit as shown in figure 2. The triode valve have three electrode 6V battery is connected to the electric bulb with rheostat. For the measurement of current and voltage the DC Voltmeter (0-10V) & DC ammeter (0 -1 A) are connected. Figure 1 3 BSCPH304 Figure 2 1.6 Procedure : For plate characteristics, perform the experiment in following steps. 1. Make electrical connection as shown in figure 2. 2. With the help of rheostat R2 adjust to minimum plate voltage. 3. Note down the plate current in milliamter. 4. Now increase the plate potential in the steps (say in 2V step) and read the corresponding plate current in milliamter. 5. Draw the graph between plate voltage and plate current, which is called plate characteristics of diode. 1.7 Observation: Table1.For plate Voltage and plate current 1 Plate Voltage Plate current Vp Volt IP mA 2 4 BSCPH304 3 4 5 6 7 8 9 10 1.8 Result: The characteristics curve of diode valve is presented in the given graph. 1.9 Precaution and source of error: 1. Sensitive voltmeter and sensitive ammeter sould be used. 2. The direction about maximum plate voltage and filament voltage by manufacturer should be strictly followed. 3. Initiallty the plate voltage should be adjusted at minimum value. 4. There should not be any fluctuation on the power. 5. Reading are taken only for space charge limited region. 6. The graphs should drawn smothly. 1.10 Summary: 1. A vacuum diode is a device which works on the principle of thermionic emission. 2. Diode has two electrode namely plate cathode. 3. There is unidirectional flow of current i.e. from plate to cathode. 4. When plate potential increases, the plate current also increase. 5. Plate current is of order milliampares flows in circuit. 1.11 Glossary ` Vacuum Tube: It is evacuated glass tube in which electrodes are fitted. 5 BSCPH304 Filament: It is a cathode, which emits electrons after heating. Rheostat: It is used to vary potential. Rectifier: It the device which convert AC into DC. Resistance: Obstruction to the flow of current. 1.12 References: 1. C. L. Arora, B.Sc. Practical Physics , S. Chand publication, Delhi. 2. C.L. Arora and P.S. Hemne, Physics for Degree students (BSc III year) , S. Chand publication, Delhi. 3. S.L.Gupta, V.Kumar A Hand book of electronics Pragati prakashan, Meerut. 4. B.L.Thereja A Hand book of electronics S. Chand publication, Delhi. 5. V.K.Mehta and Rohit Mehta, Principle of electronics S. Chand publication, Delhi. 6. S.L.Gupta, V.Kumar, Practical Physics , Pragati prakashan, Meerut. 7. https://en.wikipedia.org. 1.13 Viva-voce questions: Question1. Define the process of thermionic emission? Answer: When metal filament is heated, it emits electron from its surface.